Method for producing cold rolled rimmed steel sheet or strip having non-aging property and superior deep drawability



v fracfz/re HIROSHI YOSHIDA Filed 001;. 8, 1963 fracfure July 26, 1966METHOD FOR PRODUCING COLD ROLLED RIMMED STEEL SHEET 0R STRIP HAVINGNON-AGING PROPERTY AND SUPERIOR DEEP DRAWABILIIY d b/an/r ol'amefer 9con/co/ 50/7- avg/e ofd/e Draw/1 771roug/1 United States Patent 6Claims. (Ci. 14s i2.1

The present invention relates to a method for producing a cold rolledrimmed steel sheet or strip having a nonaging property and superior deepdrawability.

Heretofore an aluminum stabilized steel sheet has been employed as acold rolled steel sheet having superior deep drawability and non-agingproperty. However, the aluminum stabilized steel sheet is lower in yieldthan the normal rimmed steel one, which results in a higher cost.

In view of the above, I contemplate the provision of a method forproducing a cold rolled rimmed steel sheet having superior deep drawingquality as well as non-aging property by the process comprising thesteps of providing a relatively inexpensive rimmed steel as a startingmaterial, adding very small amounts of elements thereto, and subjectingthe thus produced steel to heat treatment after the cold rollingprocedure, whereby an unexpected combined effect of said additives andheat treatment is fully developed.

I have been conducting an extensive research on the beneficial effect ofsmall amounts of additives combined with the heat .treatment inconnection with the deep drawing quality and non-aging property of thecold rolled rimmed steel sheet, some results of which have been appliedfor patents.

This invention is characterized by the method comprising the steps ofproviding a molten steel containing 0.020 0.150% carbon, 0.150.60%manganese and less than 0.010% phosphorus, adding to said molten steelphosphorus and at least one element selected from the group consistingof antimony, bismuth, niobium and lead so as to produce a rimmed steelcontaining phosphorus in an amount of 0.0100.040% by weight and at leastone element selected from the said group in an amount of 0.0030.050% byweight, making a cold rolled rimmed steel sheet or strip through theknown hot and cold rolling procedures, and subjecting said cold rolledsteel sheet or strip to a decanburizing and denitriding annealing in anatmosphere effectively promoting the decrease of its carbon content lessthan 0.020%, preferably less than 0.010%, and of its nitrogen contentless than 0.0025 preferably less than 0.0010%.

The cold rolled rimmed steel sheet produced by the above mentionedprocess has a non-aging property and superior deep drawabilityrepresented by an excellent conical cup value determined by the conicalcup test specified by the Japanese Industrial Standard Z-2249.

The steel sheet of my invention has a crystallographic orientationfavorable for the deep drawing working operation together with anon-aging property in which age hardening will not take place duringstorage for an extended period of time. The crystallographic arrangementis of the socalled cube-on-corner oriented grain one in which the (111)plane is paralleled to the sheet plane. Many metallurgist-s report thatthe cube-on-corner orienta- 3,262,821 Patented July 26, 1966 tion isadvantageous for the deep drawing steel sheet, but a complete theorythereon has not been established yet. It is believed, however, that itis caused by the directionality of slip of crystal grains underdeformation.

A rimmed steel suitable for carrying out my invention is made by theprocess comprising the steps of providing a molten steel containing0.02-0.15% carbon, 0.15O.60% manganese, and less than 0.010% phosphorusin a steel making step by means of an open hearth or electric furnace,or a converter, and adding phosphorus and one or more of the elementsselected from the group consisting of antimony, bismuth, niobium andlead to produce a rimmed steel containing 0.010-0.040% phosphorus and0.003-0.050% antimony (bismuth, niobium or lead).

As disclosed in the prior patent applications referred above, phosphorusis effective for improving non-aging and deep drawing qualities.However, when the phosphorus content exceeds a predetermined amount, itwill cause the steel sheet to be hardened so that it will give an illeffect to ductility as Well as impact value after working. Therefore0.040% is preferred to be the upper limit of phosphorus. It should benoted, however, that the phosphorus content derived from a startingmaterial does no benefit for non-aging and deep drawing qualities of thesteel sheet product. It is required that phosphorus should be removedfrom the molten steel as completely as possible in the course of steelmaking process, and thereafter, a fresh quantity of phosphorus should beadded to the steel, which is one of the features of the invention. Thereason for this has not been clear, but, based on the experiments, it isnecessary that the phosphorus content of the molten steel should bethoroughly removed at least less than 0.010%.

It has been found that an addition of one or more of the elementsselected from the group consisting of antimony, bismuth, niobium andlead is not so effective for non-aging quality as that of phosphorus,but the addition of a very small amount thereof is effective fordeveloping a preferred crystallographic orientation suitable for deepdrawing in the cold rolled steel sheet of this invention. The amount tobe added is so small compared to that of phosphorus that it has beendiscovered that it is preferred in the range of 0.003'0.050%.

A steel sheet of the final gauge of this invention is produced bysubjecting the rimmed steel of the above composition to the known hotand cold rolling procedures. Then, a cold rolled steel sheet of thefinal gauge thus produced is subjected to a decarburizing anddenitriding annealing in a decarburizing and denitriding atmosphere toproduce a steel containing less than 0.020%, preferably less than 0.010%carbon and less than 0.0025%, preferably less than 0.0010% nitrogen. Thedecarburizing and dinitriding atmosphere may be of known one containing,for example, moist H added with about 10% steam or mixture of moist Hand N The annealing temperature is preferred between 500 and 750 C. Thetype of the annealing furnace is not limited. Either batch or continuoustype may be used. An open coil type annealing furnace is the mostsuitable for obtaining a uniform quality of product, and also from apoint of view of a Working hour.

Thus, carbon and nitrogen, both of which are deleterious to non-agingand deep drawing properties of steel sheet, are removed while, on theother hand, the crystallographic orientation advantageous for deepdrawing is developed.

listed E]. (percent) Chemical Composition (percent) Mechanicalproperties O.C.V. (mm.)

EXAMPLE 2 Trace Trace Chemical Analysis, Percent Chemical Analysis,Percent Annealing deep drawing and non-aging propert TABLE 1 de-C, de-

de-C, dc-N annealin ing superior the annealed strip coil is subjected toa known skin pass rolling to obtain a cold rolled rimmed steel sheethavin Specimen No. 6 of Table 1.

This steel sheet corresponds to Specimen No. 16 of A steel makingprocess similar to Example 1 is car- Then, ferro-phosphorus (20%phosphorus), metallic This ingot is subjected to the same process as de-Table 1 shows the chemical compositions and various Table 1.

position lead, and term-manganese are added to the above molten steel toobtain a rimmed steel ingot of the following composition:

having superior deep drawing and non-aging properties listed in SpecimenNo. 16 of Table 1.

mechanical properties of various kinds of known steel lOIl wi metallicFinally, 40 sheet and also of the steel sheet of this invention.

Steel Chemical Compositions, (Percent) do Aluminum stabilized steelOrdinary anncaling Rimmed steel added with P and Sb- Rimmed steel addedwith P and Bi".

Rimmed steel added with P and N b.

Thereafter, this steel scribed in Example 1 to produce a cold rolledsteel sheet hiefly of scrap and p iron is refined by the known basicopen hearth furnace process in the steel making process with a specialattenphosphorus),

Specimen No.

Speci- 1 Normal rimmed stcel Ordinary annealing.

5, do do 7 .e. do.

ing 0 EXAMPLE 1 This example corresponds to Specimen No. 6 of the 5sheet listed in Table 1.

Chemical Analysis, Percent Trace -manganese are added to the molten intoa mold to obtain a rimmed steel t of the following composition ChemicalAnalysis, Percent Trace mg composition:

-phosphorus (20% This invention is now described in connect thefollowing examples.

A steel material consist tion to dephosphorization to obtain a steel ofthe follow- 10 ried out to obtain a molten steel of the following com-Then, ferro antimony and ferro steel, and poured ingo Then, the steelingot is subjected to the known hot and cold rolling procedures toobtain a cold rolled steel strip coil of 0.8 mm. in thickness. stripcoil is subjected to a decarburizing and denitriding anneal in anatmosphere consisting of H N mixed gases, 75% H and 25% N added withabout 10% H O in an open coil type annealing furnace at the temperatureof 700 C. for a period of hours.

See footnote at end of table.

Mechanical Properties Intensity of Specimen (111) plane No. '1.S. Y.P.YE. Y.E. after Increase in diffraction (kg/mm?) (kg/mm?) (percent) 6months Y.E. during peak (percent) 6 months 1 Drawn through.

Referring to Table 1, Specimen No. 1 refers to a noris obtained. Ingeneral, as the R value depends on the mal rimmed steel sheet of thecommercial grade, No. 2 direction from which the test specimen is taken,the measto a normal rimmed steel sheet subjected to a decarurement alongthe three directions, rolling direction (R burizing and denitridingannealing, and No. 3 to an alumi- 45 degrees to the rolling direction (Rand 90 degrees num stabilized steel sheet widely employed for deep tothe rolling direction (R is made, and the mean 'i n gp ll l l refer toThe value E is obtained from the following formula: co d ro e rimmedstee s eet produced in accordance with this invention. i +2(R45) Inreference to the mechanical properties, plastic strain ratio (R),conical cup value (C.C.V.), elongation (EL), The Japanese IndustflalStandard, relatlng Erichsen cup value (EL), tensile strength (T.S.),yield point (Y.P.), yield point elongation (Y.E.), Y.E. after sixmonths, increase in Y.E. during six months, and the intensity of (111)plane diffraction peak by the X-ray inverse pole figure method areshown.

The plastic strain ratio, R, is a value showing the deep drawingproperty and the preferred orientation suitable for the deep drawabilityof the steel sheet, and can be obtained from the following formula:

log W o/W R log t /t where The greater the R value the less thinning inthe thickness direction in the plastic deformation, and the more thedeformation in the width direction.

It follows that the steel sheet material having a large R value isexcellent in the deep drawing property, since the fracture in the deepdrawing process is caused by the necking due to the decrease of sheetthickness. As a matter of fact, in obtaining the R value, it isdifficult to conduct an accurate determination of the thinning in thethickness direction. So we measured the elongation of gauge length ofthe tensile test specimen by means of the electronic strain meter andthe mean width of the specimen. The R value is obtained from thefollowing formula, provided that the volume of the deformed testspecimen being constant:

l -W -t =l-w-r where l gauge length before tension gauge length aftertension log W /W log l-w/l -w By the above measurement, the test errorsare very small. For this test specimen, a tensile test specimen (gaugelength 50 mm.) of I IS (Japanese Industrial Standard) No. 5 is employed,and the R value in 15% extension to the method of conical cup test, hasbeen recently published. In this conical cup test, it is possible todraw a steel sheet without forming wrinkles and without applying nayblankholder pressure provided the correct blank diameter is selectedwith respect only to sheet thickness. The effect of bending andunbending, which is an important factor in a cylindrical cup-formingtest, is also less important in the conical cup test. A hemisphericallyended punch with a profile radius of approximately 5 to 10 times thethickness of the test blank is used. The rating of drawability isobtained from the average diameter of the rim of the conical cup whenfracture occurs. Since the blank diameter is fixed only by the sheetthickness, the test is simple and quick.

The principle of the test is illustrated in FIG. 1. A circular blank isrested horizontally in the conical die, and drawn with the appropriatepunch until the bottom of the cup fractures. The dimensionalspecifications are given in Table 2.

The die hole diameters specified are such that no ironing of the cupoccurs as it enters the die hole. Blanks should be cleaned and thenlubricated and the speed of drawing is virtually immaterial.

The conical cup-forming test of the Japanese Industrial Standard, Z2249,is performed in an arrangement of tools for a conical cup test shown inthe accompanying drawing, in which:

FIG. 1 shows a sectional view of the arrangement of tools for theconical cup test.

FIG. 2 shows a perspective view of a shape of fractured cup as theresult of test.

FIG. 3 shows a perspective view of another shape of fractured cup.

FIG. 4 shows a perspective view of a shape of a completely drawn cupwith no fracture.

More particularly, the conical cup value (C.C.V.) is represented by thenumerical value, mm., of the average diameter of the rim of the conicalcup when fracture occurs as shown in FIGS. 2-3. The conical cup valueshown in FIG. 3, which is less than that of FIG. 2, is obtained from thesteel sheet having a better deep drawability than that of the one shownin FIG. 2. The shape of the completely drawn cup with no fracture shownin FIG. 4 is attained by the steel sheet of a very high deepdrawability, and in this case, no value of conical cup 7 test isobtained, but represented as drawn through in Table 1.

In order to obtain the conical cup value (C.C.V.) of a steel sheet of aparticular thickness, the particular tools specified by I IS Z-2249 asshown in Table 2 should be employed. C.C.V. of various steel sheetlisted in Table 1 are the measurements conducted on the sheet of thethickness, 0.8 mm. by means of the die type 17 of Table 2. In Table 3,the minimum standard value for showing the drawability of each sheet ofa particular thickness produced by the process of this invention islisted.

C.C.V. of the sheet of Sheet Thickness, mm. Die Type, 518 thisinvention.

1 Or less.

A series of tensile test, such as, elongation, tensile strength, yieldpoint, and yield point elongation, are conducted on Specimen No. 5having the gauge length, 50 mm., specified by 115. An Erichsen cup testis carried out by means of the ram head with the radius of As clearlyshown in the E value and the X-ray intensity of (111) plane diffractionpeak of Table 1, the crystallographic orientation of the rimmed steelsheet of this invention, namely, Specimen Nos. 4 to 16, is differentfrom that of the normal rimmed steel sheet.

Thus, the X-ray intensity of (111) plane'dilfraction peak of the normalrimmed steel sheet is small while that of the steel sheet produced fromthe normal rimmed steel which has been subjected to the decarburizingand denitriding annealing is also relatively small.

Compared to the above, the accumulation of the main crystallographicorientation (111) of the steel sheet of this invention is stronger.

The intensity of (111) plane diffraction peak of the aluminum stabilizedsteel is stronger than that of the normal rimmed steel, but weaker thanthat of the steel sheet of this invention. The above-mentioned re'lationship is made more distinct in the E value of Table 1. Thus, the E valueof the normal rimmed steel is the least of all, that of the decarburizedand denitrided rimmed steel larger, and that of the aluminum stabilizedsteel the largest. The E value of the steel sheet of this invention isalso equal to or larger than that of the aluminum stabilized steel.

In case (111) plane is parallel with the rolling surface, the fact thatthe E value is made large can be explained theoretically as follows:when the slip direction is only (111) direction while deformation, andwhen (111) plane is parallel with the rolling surface, it is explainedby mathematical analysis that the strain in the sheet plane directionbecomes larger than that in the thickness direction.

In Table 1, the conical cup value of the rimmed steel sheet of thisinvention is good, and particularly, the test Specimens of No. 6, 7, 10,11 and 16 are drawn through without fracture, respectively.

As described hereinabove, a favorable effect of phosphorus and antimony,bismuth, niobium or lead on the deep drawing quality of the steel sheetis apparent. However, in the practical press forming process, theformation of miscellaneous complicated shapes is required so much thatnot only the high degree deep drawability but also the high stretchformability should be given to the steel sheet. In reference to thecharacteristic value for showing stretch formability, both elongation,El., and the Erichsen cup value, Er., are universally adopted.

As clearly illustrated in Table 1, the steel sheet of this invention hasa good conical cup value and Ti value as well as good El. and Er.values.

The test value for showing an aging property of steel sheet is shown bythe change of yield point elongation of a test sheet left for a periodof six months. As clearly illustrated in Table 1, the increase in yieldpoint elongation of the steel sheet of this invention is hardly observedor so small that the non-aging quality thereof is as excellent as thatof the aluminum stabilized steel sheet well known for its non-aging.

Various changes and modifications of this invention can be made and, tothe extent that such variations incorporate the spirit of thisinvention, they are intended to be included within the scope of theappended claims.

I claim:

1. A method for producing a cold rolled rimmed steel sheet or striphaving non-aging property and superior deep drawability comprising thesteps of: (1) providing a molten steel containing 0.0200.150% carbon,0.15- 0.60% manganese, less than 0.010% phosphorus and the remainderbeing essentially iron, (2) adding to said molten steel phosphorus andat least one element selected from the group consisting of antimony,bismuth, niobium and lead so as to produce a rimmed steel containingphosphorus in an amount of 0.010-0.040% and at least one elementselected from the said group in an amount of 0.0030.050%, (3) forming arimmed steel sheet or strip by hot and cold rolling, and (4) subjectingsaid cold rolled steel sheet or strip to a decarburizing and denitridingannealing to decrease the carbon content to less than 0.020% and thenitrogen content to less than 0.0025

2. The method according to claim 1 wherein the decarburizing decreasesthe carbon content to less than 0.010%.

3. The method according to claim 1 wherein the denitriding decreases thenitrogen content to less than 0.0010%.

4. A cold rolled rimmed steel sheet or strip having nonaging propertyand superior deep drawability consisting essentially of less than 0.020%carbon, 0.150.60% manganese, 0.010-0.040% phosphorus, 0.003-0.050% of atleast one element selected from the group consisting of antimony,bismuth, niobium and lead, less than 0.0025% nitrogen, and the remainderbeing essentially iron.

5. The steel sheet or strip in accordance with claim 4 wherein thecarbon content is less than 0.010%.

6. The steel sheet or strip in accordance with claim 4 wherein thenitrogen content is less than 0.0010%.

References Cited by the Examiner UNITED STATES PATENTS 3,188,246 6/1965Olt et a1 14816 3,193,417 7/1965 Kopchak 14831 3,215,567 11/1965 Yoshida148-31 DAVID L. RECK, Primary Examiner.

H. F. SAITO, Assistant Examiner.

1. A METHOD FOR PRODUCING A COAL ROLED RIMMED STEEL SHEET OR STRIPHAVING NON-AGING PROPERTY AND SUPERIOR DEEP DRAWABILITY COMPRISING THESTEPS OF: (1) PRIVIDING A MOLTEN STEEL CONTAINING 0.020-0.150% CARBON,0.150.60% MANGANESE, LESS THAN 0.010% PHOSPHORUS AND THE REMAINDER BEINGESSENTIALLY IRON, (2) ADDING TO SAID MOLTEN STEEL PHOSPHORUS AND ATLEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF ANTIMONY,BISMUTH, NIOBIUM AND LEAD SO AS TO PRODUCE A RIMMED STEEL CONTAININGPHOSPHORUS IN AN AMOUNT OF 0.010-0.040% AND AT LEAST ONE ELEMENTSELECTED FROM THE SAID GROUP IN AN AMOUNT OF 0.003-0.050%, (3) FORMING ARIMMED STEEL SHEET OR STRIP BY HOT AND COLD ROLLING, AND (4) SUBJECTINGSAID COLD ROLLED STEEL SHEET OR STRIP TO A DECARBURIZING AN DENITRIDINGANNEALING TO DECREASE THE CARBON CONTENT TO LESS THAN 0.020% AND THENITROGEN CONTENT TO LESS THAN 0.0025%.